Add_elements_by_function

<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.5/d3.min.js"></script>
  <style>
    body { margin:0;position:fixed;top:0;right:0;bottom:0;left:0; }
    svg { width:100%; height: 100% }
  </style>
</head>

<body>
  <script>
    var x = 10, y = 30, width = 600, height = 480;
    function drawCircles(svg, data) {
      var circles = svg.selectAll('circle').data(data);
      circles.enter().append('circle')
        .attr('r', 3);

circles.exit().remove();

circles
        .attr('cx', function(d) { return d.x })
        .attr('cy', function(d) { return d.y });
    }
    numPoints =272;
    var data = [];
    for (var i = 0; i < numPoints; i++) {
      data.push({
        x: Math.random() * (width-3) + (x),
        y: Math.random() * (height-1) + (y)
      });
    }
    var svg = d3.selectAll('svg').data([0]);
    svg.enter().append("svg");
    svg.append("rect")
      .attr({x: x, y: y, width: width, height: height})
      .style({ fill: "#a72d1a"})
      .transition().duration(3000).ease("bounce")
      .style({ fill: "#5db9e3"})
		drawCircles(svg, data);
    console.log(data);
  </script>
</body>

https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.5/d3.min.js